People with age-related macular degeneration (ARMD) and similar diseases affecting the ocular media have long retinal adaptation times leading to poor visual acuity during adaptation. Dark adaptation times may be measured in tens of minutes in typical cases. The lack of visual acuity may cause serious mobility problems in people with ARMD, especially near curbs and steps in bright sunlight. Generally, there are problems in the aged relating to contrast sensitivity in varying lighting conditions leading to vision problems while driving during the night time.
Ophthalmologists have long sought a prescriptive solution wherein the ARMD patient may be fitted with light absorbing eyeglasses that restrict the amount of light reaching the patient's eyes thereby increasing visual acuity. More particularly, ophthalmologists have sought prescription eyeglasses. Ophthalmologists have also sought eyeglasses that are capable of adapting to a wide range of lighting conditions, ranging from the office environment in which light luminance levels are typically on the order of 12-18 cd/m2 to a bright sunny day outside, in which luminance levels may be on the order of 5000 cd/m2. Ophthalmologists have further sought prescription eyeglasses that can respond quickly to keep the retinal illumination level near an ideal value such that dark adaptation effects are not impaired and retinal bleaching does not occur.
While light absorbing eyeglasses exist in the prior art, they contain fundamental flaws. One major flaw is the inability of the ophthalmologist to adjust for patient-to-patient variations of dark to bright transmission ranges, and for the patient's overall illumination response. Secondly, the control group studies of subject response to light absorbing eyeglasses were made according to Ross, et al., in “Design and Evaluation of Liquid Crystal (LC) Dark Adapting Eyeglasses for Persons with Low Vision”, Final Report, Project #C776-RA, Atlanta V.A. Rehab Center, March 1997, indicating that subjects preferred to maintain some control over the lens behavior of the light absorbing eyeglasses. Ophthalmologists have therefore sought eyeglasses that allow for limited patient manual override.
Adjustable variable transmissivity (AVT) eyeglasses may be useful for sports applications, occupational applications and medical applications apart from ARMD. For medical use, AVT eyeglasses may be useful in the treatment of retinal pigmentosa, ocular albinism, choroidermia, gyrate atrophy, corneal scarring, cataracts and ureitis. A variety of outdoor sporting activities including fishing, hunting, skiing, golf and baseball may benefit from AVT eyeglasses. Occupational safety applications that involve driving, heavy equipment operation, low light military or police maneuvers, oxyacetylene welding and glassblowing may further benefit from AVT eyeglasses.